PROJECT SUMMARY/ABSTRACT Cholera is an acute diarrheal disease that affects 3-5 million people each year. Cholera is caused by Vibrio cholerae; a Gram-negative bacterium and facultative human pathogen that is native to aquatic ecosystems around the world. The worldwide distribution of V. cholerae makes it a significant health threat anytime human populations lack access to clean water and good sanitation; a fact exemplified by the ongoing cholera epidemics in Haiti and Yemen. The devastating consequences of cholera combined with the rapidity with which it can spread, evolving antibiotic resistance, and its ability to persist in aquatic ecosystems, have underscored the need for the development of novel approaches to limit the spread of this epidemic disease. We recently discovered that cellular metabolites produced by V. cholerae can serve as environmental cues to downregulate the production of the virulence factors cholera toxin and the toxin coregulated pilus. In this proposal, we will investigate how cell metabolites and other environmental signals modulate transcriptional responses involved in the V. cholerae life cycle. Two specific aims are proposed. The first aim will characterize the role of the LysR-family transcriptional regulator LeuO in V. cholerae pathogenesis and environmental adaptation. The second aim will investigate how the membrane-bound transcriptional regulator ToxR senses and responds to environmental stimuli. Determining the regulatory mechanisms and environmental cues that modulate adaptive responses will illuminate important aspects of V. cholerae pathogenesis, provide a better understanding of the factors that contribute to the epidemic spread, and may lead to the development of novel approaches to combat the disease cholera.